The present invention relates to a hydraulic chuck and clamping methods, wherein a sleeve is radially deformed to grip an element, such as a tool shank.
Numerous types of chucks have been devised for securely holding tools. Among those are so-called hydraulic chucks, which include a deformable center cylindrical bore for clamping a tool shank. Extending around the bore in radially spaced relationship thereto is a groove filled with an incompressible medium, such as oil. The portion of the chuck between the groove and the bore constitutes a radially deformable sleeve. A pressurizing member, such as a screw (i.e., a threaded piston), communicates with the oil to pressurize the oil when the screw is advanced. In response to the oil being pressurized, the sleeve is deformed in a manner reducing the effective diameter thereof, i.e., reducing the effective inner diameter of an inner wall of the bore, whereby the wall grips the tool shank. When the screw is retracted to depressurize the oil, the sleeve restores itself to its original shape to release the tool shank. Examples of hydraulic chucks are described in U.S. Pat. Nos. 4,387,906; 4,677,792; and 5,127,780.
A shortcoming of such chucks is that the pressure must be maintained during use of the tool. In the event of a pressure failure (e.g., oil leakage), the tool can become accidentally released during use, which not only interrupts the work, but can present a safety risk as well.
Also, the sleeve is typically a thin-walled sleeve, which presents certain additional risks. For example, if the pressure is applied without a tool being present, the sleeve is subjected to excessive deformation, which, over time, can produce enough fatigue to cause breakage (splitting) of the sleeve. If the pressure is applied with a tool only partially inserted, the location where the sleeve contacts an inner edge of the tool shank can have a ridge permanently formed therein. Another type of undesirable deformation can result if the outer surface of the tool shank includes a flat, because the area where the flat is disposed will not offer resistance to the deformation of the wall; hence a flat can become formed in the sleeve.
It is, therefore, an object of the invention to provide a reliable yet relatively inexpensive way of avoiding accidental release of the clamped member.
Another object is to provide a chuck and a clamping method wherein a chuck has a deformable sleeve, which is not prone to breakage or permanent deformations.
The present invention relates to a hydraulic chuck comprising a chuck body extending in a longitudinal direction and including radially spaced inner and outer surfaces. The inner surface defines a wall of a bore having a longitudinally extending axis. The outer surface is spaced from the bore wall in a direction extending radially outwardly with respect to the axis. At least one closed cavity is disposed in the chuck body in radially spaced relationship to the bore wall and the outer surface. The cavity extends circumferentially by a distance less than the circumference of the chuck body and contains an incompressible medium. A pressurizing device communicates with the medium for pressurizing the medium to radially deform and expand the bore wall from a normal diameter to a larger diameter for enabling a member to be moved into or from the bore. A depressurizing of the medium causes the bore wall to radially retract to the normal diameter for clamping the movable member in the bore.
Preferably, the bore wall includes a longitudinal recess at a location adjacent the at least one cavity.
Preferably there is a plurality of the cavities, and the cavities are interconnected.
The cavities, which can be circumferentially spaced apart and/or radially spaced apart, may have a circular cross-section or a non-circular cross-section.
The invention also pertains to a method of clamping a member utilizing the above-described hydraulic chuck.